1. Field of the Invention
The present invention relates to a signal analysis circuit for a supplying-end module of an induction type power supply system, and more particularly, to a signal analysis circuit capable of analyzing a coil signal to retrieve a trigger signal in a supplying-end module of an induction type power supply system.
2. Description of the Prior Art
For safety purposes, a power supply device of an induction type power supply system has to ensure that a proper power receiving device is positioned on the sensing area of a supplying-end coil of the power supply device, and that the power receiving device is ready to receive power before the power is supplied. In order to allow the power supply device to confirm the above conditions, a data code should be transmitted for identification purposes. The data code transmission is performed via the following steps: the power supply device drives the supplying-end coil to generate resonance and sends electromagnetic power to the power receiving device in order to transmit power. When the power receiving device receives the power, the power receiving device may change the impedance on the receiving-end coil via the signal modulation technology, and the variations are fed back to vary the amplitude of carriers on the supplying-end coil. The signals of the supplying-end coil are then converted into digital information to be transmitted to a supplying-end microprocessor for interpretation via a circuit.
The signal variations fed back to the supplying-end coil via the abovementioned modulation technology are demodulated by a signal analysis circuit in the supplying-end module. Since the coil signal is an alternating circuit (AC) signal with a larger voltage such as several tens or hundreds of volts while the modulation signal is an amplitude variation on the AC signal and is far smaller than the amplitude of the coil signal, the AC coil signal cannot be directly processed by the processor and should be converted to be within a voltage range via the signal analysis circuit, where the voltage range is able to be processed by the processor. In U.S. Publication No. 2013/0342027 A1, the signal analysis circuit includes a clamping circuit in its front end. The clamping circuit clamps the signal to a higher voltage, and the signal analysis circuit then performs rectification and low-pass filtering on the signal to generate a signal interpretable by the processor.
The above circuit structure in the prior art still has some drawbacks, however. Please refer to FIG. 1, which is a waveform diagram of a supplying-end coil of an induction type power supply system. As shown in FIG. 1, waveforms W1_1 and W1_2 are driving signals on both terminals of the supplying-end coil received from a driving circuit, respectively, where the waveforms W1_1 and W1_2 are rectangular waves and inverse to each other. A waveform W1_3 is a voltage signal on the coil. Ideally, the coil signal should be a sine wave continuously oscillating. As shown by the waveform W1_3, however, the coil signal appears to be an ideal sine wave in the positive half cycle and negative half cycle, but a voltage discontinuity appears when the waveforms W1_1 and W1_2 of the driving signals are switched (i.e., the boundary between the positive half cycle and the negative half cycle). The voltage difference of the voltage discontinuity is substantially equal to the amplitude of the driving signals. Note that the coil sends the power by oscillating, but the occurrence of voltage discontinuity cannot generate oscillation to deliver power. This decreases the power emission capability of the coil. In other words, the coil signal includes two parts: one is a sine-wave signal generated by coil resonance and the other is composed of the voltage discontinuity in the driving signals. However, the processor cannot interpret the effective sine wave component in the coil signal; hence, the processor may wrongly determine that the oscillation voltage on the coil is too high during power adjustment, and thus perform erroneous adjustment. In addition, when the driving voltage increases, the ratio of the sine wave signal in the coil signal may be reduced; this increases the difficulty of interpreting the modulation signal.
In U.S. Publication No. 2013/0342027 A1, the high-voltage signal from the coil may be outputted to the clamping circuit first. This signal, which directly enters the diode of the clamping circuit without being attenuated, may damage the diode due to an over-high voltage. In its signal analysis circuit, the front-end stages are operated in higher voltages and the operating voltage is reduced gradually toward the back-end stages. When a circuit element inside the signal analysis circuit is damaged, an unexpected high voltage may enter the supplying-end processor and damage it. If the supplying-end processor is burnt out, the safety control of the power supply system may malfunction. On the other hand, the signal analysis circuit in the prior art does not have signal amplification capability. In order to obtain a larger signal variation, the attenuation ratio of the coil signal should be as reduced as possible. In such a condition, the circuit elements need to endure a higher voltage, and thus are easily burnt or have decreased life. Furthermore, since the signal analysis circuit has only the signal attenuation capability but cannot perform amplification on signals, tiny signal variations are hard to be interpreted.
Thus, there is a need to provide a new signal analysis circuit, in order to obtain a better signal analysis performance and also prevent the above problems.